<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<style>
  body>div{
    width: 200px;
    border: 1px solid red;
    overflow: hidden;
  }
  div>div{
    width: 50px;
    height: 50px;
  }
  #d1{
    background-color: red;
    float: left;
  }
  #d2{
    background-color: green;
    float: left;
  }
  #d3{
    background-color: blue;
    float: left;
  }
  p{
    width: 100px;
    height: 100px;
    background-color: pink;
  }
  ul{
    list-style-type: none;
    margin: 0;
    padding: 0;
      overflow: hidden;
  }
  li{
      float: left;
      margin-right: 20px;
  }
</style>
<body>
<ul>
  <li><a href="">首页</a></li>
  <li><a href="">免费课</a></li>
  <li><a href="">直播课</a></li>
  <li><a href="">线上班</a></li>
  <li><a href="">线下班</a></li>
</ul>
<div>
  <div id="d1"></div>
  <div id="d2"></div>
  <div id="d3"></div>
</div>
<p></p>
</body>
</html>